The present invention relates to an optical-information-reading apparatus which reads a code symbol such as a barcode and a two-dimensional code.
The bar code, which is one-dimensional code information, is well known for use in merchandise management, inventory management, and the like. Further, the two-dimensional code has been known as a code having higher information density. A processing method has been known, according to which the two-dimensional code is imaged by a solid-state image sensing device, such as CMOS image sensor or CCD image sensor, as a device for imaging the two-dimensional code, after which various kinds of processing are performed on the image, and it is binarized and decoded.
The CMOS image sensor used in such an apparatus to read the code information has been not different from the one used for a digital camera, or the like, in a function so that it is required also to have function as a camera to normally take photographs of an object and/or a sight. For example, in the case of the inventory management, it is used when a target object and a location in which the object is stored are imaged, which are stored in a database together with code information.
A small-scaled camera using the above-mentioned CMOS image sensor is equipped for a mobile phone. The mobile phones have a camera function to take photographs of an object and/or a sight like the normal digital camera and mostly include a scanner for barcode/two-dimensional code and an optical character reader (OCR).
In a scene of the above-mentioned merchandise management, inventory management or the like, it is necessary to scan code symbols applied to objects, one object after another. At present, it is desirable to provide an autofocus function, and the autofocus function and the imaging process are required to be fast.
Generally, according to a method in wide use, a lens is arranged so as to move along an optical axis, the distance at which it focuses on the code symbol is calculated, and the lens moves to a position that is suitable for the distance (see, for example, Patent Document 1 below). Further, a simple autofocus is in wide use according to which two lens locations of short and long ranges, in addition to a fixed lens location, are stored in a memory and, when failing to image, the lens moves in a direction of the short range or the long range (see, for example, Patent Document 2 below).
Further, an optical reading apparatus has been equipped with technology such that optical wavefront modulation elements combining a plurality of lenses are formed to have a focusing function, and focus is adjusted based on the distance to a reading target object (see, for example, Patent Document 3 below).
Additionally, technology has been disclosed such that an image lens, a prism, a lens for long range and its image sensor, and a lens for short range and its image sensor are combined to form optics, and focal distance is adjusted without moving the lenses (see, for example, Patent Document 4 below).